1. Field of the Invention
The present invention relates to an organic light emitting display OLED. More particularly, the present invention relates to an OLED capable of improving the quality of an image by using an auxiliary electrode.
2. Discussion of the Background
Recently, technologies related to devices for a display apparatus have become important. In this regard, an OLED has been spotlighted as a display apparatus capable of displaying natural colors.
The OLED includes a cathode, an anode, and an organic light emitting layer formed between the cathode and the anode. The organic light emitting layer is disposed between a conductive electrode having a high work function and a conductive electrode having a low work function to generate light, so that an image is displayed. Generally, in the OLED, the conductive electrode having the high work function is used as an anode, through which holes are injected into the organic light emitting layer, and the conductive electrode having the low work function is used as a cathode, through which electrons are injected into the organic light emitting layer.
One electrode of the OLED includes transparent material, which rarely absorbs light in a wavelength band of emitted light, to emit the light out of the OLED.
The principle of the OLED having the electrodes described above is as follows. As the holes and electrons are injected into the organic light emitting layer through the anode and the cathode, respectively, excitons are generated in the organic light emitting layer. When the holes and the electrons combine, the excitons are emitted and decay with light having a particular wavelength that is generated corresponding to the differential energy between the lowest unoccupied molecular orbital LUMO and the highest occupied molecular orbital HOMO.
The cathode or the anode, through which light forming an image travels, is prepared as a transparent electrode.
However, when the transparent electrode is formed on the entire surface of a display unit, the transparent electrode should be thinly formed to increase light transmittance and to protect the organic light emitting layer. Thus, resistance on an entire surface of the transparent electrode may not be uniform, so that a voltage drop may occur.
Additional auxiliary electrodes may be provided outside each pixel to overcome the voltage drop. However, an aperture ratio of the pixel may be reduced because additional spaces are used for the auxiliary electrodes.